Isonoe ( /aɪˈsɒnɵʊiː/ eye-SON-o-ee; Greek: Ισονόη), also known as Jupiter XXVI, is a retrograde irregular satellite of Jupiter. It was discovered by a team of astronomers from the University of Hawaii led by Scott S. Sheppard in 2000, and given the temporary designation S/2000 J 6.

Isonoe is about 3.8 kilometres in diameter, and orbits Jupiter at an average distance of 23,833 Mm in 751.647 days, at an inclination of 166° to the ecliptic (169° to Jupiter's equator), in a retrograde direction and with an eccentricity of 0.166.

It was named in October 2002 after Isonoe, one of the Danaides in Greek mythology, and a lover of Zeus (Jupiter).

Isonoe belongs to the Carme group, made up of irregular retrograde moons orbiting Jupiter at a distance ranging between 23 and 24 Gm and at an inclination of about 165°.

The Moon is the only natural satellite of the Earth, and the fifth largest satellite in the Solar System. It is the largest natural satellite of a planet in the Solar System relative to the size of its primary, having a quarter the diameter of Earth and ¹⁄₈₁ its mass. The Moon is the second densest satellite after Io, a satellite of Jupiter. It is in synchronous rotation with Earth, always showing the same face; the near side is marked with dark volcanic maria among the bright ancient crustal highlands and prominent impact craters. It is the brightest object in the sky after the Sun, although its surface is actually very dark, with a similar reflectance to coal. Its prominence in the sky and its regular cycle of phases have, since ancient times, made the Moon an important cultural influence on language, calendars, art and mythology. The Moon's gravitational influence produces the ocean tides and the minute lengthening of the day. The Moon's current orbital distance, about thirty times the diameter of the Earth, causes it to appear almost the same size in the sky as the Sun, allowing it to cover the Sun nearly precisely in total solar eclipses.